1. Field of the Invention
The present invention relates to an image display apparatus, and more particularly, to an image display apparatus for displaying images of a plurality of kinds of video signals such as an NTSC (National Television System Committee) video signal, a PAL (Phase Alternating by Line) video signal, a SECAM (Sequential Memoire Color television System) video signal, or the like.
2. Description of the Prior Art
Currently, there are used various kinds of video signals such as the NTSC video signal, the PAL video signal, the SECAM video signal or the like, wherein the number of scanning lines of one kind of video signal may be different from that of another kind of video signal and the field frequency of one kind of video signal may be different from that of another kind of video signal. For example, the NTSC video signal has 525 horizontal scanning lines and a field frequency of 60 Hz, and each of the
video signal and the SECAM video signal has 625 horizontal scanning lines and a field frequency of 50 Hz. In this specification, a horizontal scanning line is referred to as a scanning line hereinafter.
Generally speaking, a display apparatus for displaying a first kind of video signal thereon can not display a second kind of video signal which is different from the first kind of video signal. For example, a display apparatus for displaying the NTSC video signal can not display the PAL video signal. However, there has been developed and sold a conventional multi-system type television set capable of receiving and demodulating broadcast waves which are respectively modulated according to a plurality of kinds of video signals, and displaying one kind of video signal selected from among the demodulated video signals.
FIG. 1 shows a conventional multi-system type television set of this type. In FIGS. 1 and 2, only circuits for processing a video signal are shown. Since circuits for processing an audio signal are constituted in a manner similar to that known to those skilled in the art, these circuits have been omitted in the drawing figures and the specification of the present application.
Referring to FIG. 1, broadcast waves which are modulated according to an NTSC video signal, a PAL video signal and a SECAM signal are received by an antenna 100, and then, are inputted to a television tuner 101. The television tuner 101 comprises a high frequency amplifier and a frequency converter, and amplifies and converts the received broadcast waves into video intermediate frequency signals (referred to as VIF signals hereinafter) of the NTSC, PAL and SECAM video signals, respectively, to output the VIF signals through contacts (a), (b) and (c) of a switch SW1 to VIF amplifiers and demodulator 102a, 102b and 102c for the NTSC, PAL and SECAM video signals.
Switches SW1 to SW7 are provided for selecting the broadcast waves of the respective signals, and are manually switched over by the operator interlocking with each other. In case of receiving the broadcast wave of the NTSC video signal, the switches SW1 to SW5 are switched over to respective contacts (a) thereof and the switches SW6 and SW7 are switched over to respective contacts (b) thereof. In case of receiving the broadcast wave of the PAL video signal, the switches SW1 to SW5 are switched over to respective contacts (a) thereof and the switches SW6 and SW7 are switched over to respective contacts (a) thereof. In case of receiving the broadcast wave of the SECAM signal, the switches SW1 to SW5 are switched over to respective contacts (c) thereof and the switches SW6 and SW7 are switched over to respective contacts (a) thereof.
Each of the VIF amplifiers and demodulator 102a, 102b and 102c has a VIF amplifier and a demodulator for each corresponding video signal, and outputs a video signal including a luminance signal, a color signal and synchronizing signals through the either one of contacts (a), (b) and (c) of the switch SW2 and a common terminal thereof to the contact (a) of the switch SW10 provided for manually selecting either one of a video signal outputted from either one of the outputs from the VIF amplifiers and demodulator 102a, 102b and 102c, and video signals inputted through external input terminals 103a and 103b from external units such as video tape recorders, video disc players, video cameras or the like. The external input terminal 103a is connected to the contact (b) of the switch SW10, and the external input terminal 103b is connected to the contact (c) of the switch SW10. A common terminal of the switch SW10 is connected through either one of the contacts (a), (b) and (c) of the switch SW3 to either one of respective input terminals of Y/C separation circuits 104a, 104b and 104c for the NTSC, PAL and SECAM video signals, respectively.
Each of the Y/C separation circuits 104a, 104b and 104c separates an analog luminance signal Y including the synchronizing signals and an analog color signal C from the inputted video signal, outputs the separated luminance signal Y including the synchronizing signal through either one of the contacts (a), (b) and (c) of the switch SW4 to a RGB matrix circuit 105 and a synchronizing separation circuit 108, and also outputs the separated color signal C through either one of the contacts (a), (b) and (c) of the switch SW5 to the RGB matrix circuit 105. The RGB matrix circuit 105 generates R (red), G (green) and B (blue) image signals (referred to as RGB image signals hereinafter) in response to the analog luminance signal Y and the analog color signal C, and outputs the RGB image signals to a CRT display unit 106 having a deflection yoke 107.
On the other hand, the synchronizing separation circuit 108 separates and reproduces horizontal and vertical synchronizing pulses HSP and VSP from the inputted analog luminance signal Y, and outputs them through either one of the contacts (a) and (b) of the switch SW6 to either one of deflection signal generators 109a and 109b, respectively. In response to the synchronizing pulses HSP and VSP, the deflection signal generator 109a generates deflection signals having a field frequency of 50 Hz and 625 scanning lines, i.e., horizontal and vertical pluses for deflection of display in the CRT display unit 106, and outputs them through the contact (a) of the switch SW7 to the deflection yoke 107 of the CRT display unit 106. On the other hand, in response to the synchronizing pulses HSP and VSP, the deflection signal generator 109b generates deflection signals having a field frequency of 60 Hz and 525 scanning lines, i.e., horizontal and vertical pluses for deflection of display in the CRT display unit 106, and outputs them through the contact (b) of the switch SW7 to the deflection yoke 107 of the CRT display unit 106. Then, the CRT display unit 106 displays an image of the selected video signal thereon with a deflection frequency corresponding to the field frequency and the number of the scanning lines of the kind of the video signal to be displayed.
However, in the above-mentioned conventional multi-system type television set, there are provided the deflection signal generators 109a and 109b for generating the horizontal and vertical pulses (H and V Pulses) for deflection of display using an analog process. Therefore, the deflection signal generators 109a and 109b have complicated structures, respectively, resulting in an expensive cost thereof.
Further, since the CRT display unit 106 having a predetermined specification displays images of a plurality of kinds of video signals having field frequencies different from each other and having numbers of scanning lines different from each other, it is extremely difficult to correct for convergence and geometric distortions such as the so-called bobbin winder distortion or the like which may be caused therein, resulting in deteriorating a quality of displayed image on the CRT display unit 106.